FAST Cache and Naviseccli

FAST (Fully Automated Storage tiering ) Cache as all you know is a new feature introduced with Clariion FALRE R30 and VNX systems, in which we are making use of high speed FLASH drives to be configured as cache. There are a lot of things to consider while selecting the number/size/slots for FLASH drives for using as FAST cache drives. You may find many useful documents/best practices from support.emc.com in knowledgebase solutions and whitepapers.

In this post, I am trying to share some useful naviseccli commands which can be used for modifying/viewing FAST Cache configuration.

Here we have added the disks 3_0_1, 2_1_1, 1_0_1 and 4_2_1 to a FAST Cache configuration with RAID 1 and mode will be Read/Write. Here as we have added drives in this order, 3_0_1 as the primary disk for the first RAID 1 group (i.e, mirror) and 2_1_1 as the secondary. Similarly, 1_0_1 and 4_2_1 will be the primary and secondary for the second RG. This allows us to create mirrors with primary and secondary disks as intended (if available, on different buses). Thus the order in which disks are added via CLI is important.

options disks/status/perfData can be used for displaying only the required content, like disks used/status of FAST Cache etc…

Destroying a FAST Cache

cache -fast -destroy [-o]

The command -destroy can be used to destroy the FAST Cache configuration. On entering the command, you will be prompted for confirmation (-o can be used to proceed without confirmation) and once given yes, your configuration will get destroyed.

If the ‘dirty data’ in the FAST cache are more, it will take time for clearing the dirty content and then deleting the FAST cache. In that case (of higher dirty data) ,we can go for flushing the FAST Cache first. If it is not urgent to clear the dirty data (flush the cache) this activity can be planned for off-peak hours. Your performance may suffer as flushing generates a huge amount of write I/O in addition to the host I/O.

For flushing FAST cache, we can use the below commands,

For RAID Group LUNs(FLARE LUNs) :

naviseccli chglun -l lun -fastcache 0

Where lun is the LUN ID on which the FAST cache to be disabled. In RG LUNs, the FAST Cache can be managed on per LUN basis.

For Pools :

naviseccli storagepool -modify -id poolID -fastcache off

Where poolID is the the ID of the Pool on which the FAST cache to be disabled. In Storage Pools the FAST Cache can be managed on per pool basis only.

These commands causes forced flushing and thus the dirty data gets cleared in a short time. Once these are done, we can destroy the FAST Cache using the destroy command. These commands can be used for flushing the cache (if you are not destroying the FAST Cache also)

6 Responses to FAST Cache and Naviseccli

I’m wondering what happens when you decide that your current FAST Cache is not big enough and you decide to add disks. So you have to destroy the FAST Cache and create a new one with more SSDs. However: will the LUNs and pools that had FAST Cache enabled automatically have it enabled or do I need to check the settings all over again for all traditional LUNs and pools?

Hi Rob, thanks for your comment and in fact it is a very good question.
As you mentioned modifying the FAST Cache will need a reconfigure (destroy, create and configure). For destroying the FAST Cache it is better to disable the same on all the LUNs and Pools (flushing as mentioned above,will do the same). Thus when you do recreate and configure, you have to enable the same on each LUN/Pool as required (it would be better to note the configuration or take an SPcollect prior deleting the config).

Thanks for the detail insight. I have a query, while we want to reconfigure the cache, added EFD drives & installed across several bus, Force flushed the data, disabled fast cache on the pools, deleted the Fast Cache & reconfigured it, Can this process be performed online, I understand it has to be done off business hours, but will storage be still serving the data ? I also want to know, will the System Cache (DRAM) will also get disabled in this process ?